1. Field of Invention
The invention relates generally to network analyzers, and more specifically to synchronizing distributed systems for monitoring and analysis.
2. Description of Related Art
Local Area Network (LAN) analysis instruments are used to measure, characterize and test data streams on LAN systems. A prior art analyzer can have a control port that allows a remote entity, typically a personal computer (PC) executing the appropriate analysis software, to control the analyzer. The connection between the PC and the analyzer is usually a physical communications link, such as an RS-232 (presently referred to as an EIA/TIA 232) serial port, or a 10/100 megabits per second Ethernet link.
Certain tests, using test systems including two or more LAN analyzers, require that a test be started and stopped on multiple system analyzers at the same time. This requirement ensures that the data gathered from multiple data streams can be correlated together. Moreover, the internal timers of the multiple analyzers need to be synchronized together to ensure that time references from multiple measurements can be correlated.
Prior art systems for synchronization of distributed network analyzers include special and distinct cabling to provide the appropriate electrical signals between analyzers in a collection of analyzers for a particular network. The prior art cabling is also designed for specific analyzer requirements. For example, the Wandel & Goltermann Technologies, Inc., (located in Research Triangle Park, N.C.) DA-30 network analyzer provides clock synchronization and counter coordination by placing two analyzers in the same cabinet with the controller computer. The controller computer's clock is used to run both analyzers.
The network analyzers described in U.S. Pat. Nos. 5,535,193 and 5,590,116 operate most effectively when a bus, completely separate from the network to be analyzed, interconnects the analyzers. The bus for these systems preferably comprises several multiconductor computer cables that extend between parallel ports on each analyzer and the compatible port of the control computer, forming a daisy-chain parallel connection.
One disadvantage of the prior art occurs for daisy-chained, or bussed analyzers because these configurations place a limit on the number of analyzers that can be physically connected. For example, certain bus structures such as Small Computer System Interface (SCSI) buses, or IEEE 488 instrumentation buses limit the number of analyzers based on current drive and voltage limitations. For example, SCSI buses typically accommodate no more than eight analyzers. Prior art systems also typically use separate cables for control and clock information.